Polypropylene high strength yarns are usually produced by melt spinning. The polypropylene resin is heated and melted by adding it to a vertical or horizontal screw extruder, extruded by a spinneret through a metering pump, and cooled into a fiber in air. Industrially, membrane splitting and fibrillation are used to produce split and split fiber.
The characteristics of polypropylene high-strength yarn melt spinning are as follows: 1 Generally, a single-head pitch screw extruder is used. In order to adapt to the high melt viscosity and poor fluidity of the fiber-reinforced polypropylene, the screw compression ratio is large, the minimum is 2.8, and the metering section is exhausted. It may be short, and the screw length to diameter ratio ranges from 20 to 26. 2 Due to the large molecular weight, the melt temperature during spinning is generally higher than the melting point by 100 to 130 ° C, and a method such as adding a molecular weight regulator may be employed to lower the spinning temperature. 3 The crystallization speed is faster during the cooling molding process, and the cooling temperature should be slightly lower.
Polypropylene high-strength yarn has been used for short-spinning or shrink-spinning, that is, the cooling process after the melt-out of the spinneret is short, and the tunnel can be less than 1 m. For example, a 1 kt staple fiber production line can be placed in a factory with a height of 8 m and a length of 30 m from the steps of spinning, drawing, shaping, crimping and cutting. The investment is low, the efficiency is high, and the cost is reduced.
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